Changes needed to enable Python 3.12

[scarlehoff]

We have a number of dependencies that would be blocking us from using Python 3.12:

• The MultiDense layer is not compatible with Tensorflow 2.16 (MultiDense doesn't work with Tensorflow 2.16 / py3.12 #1968) (fixed in Fix multidense compatibility with tf 2.16 and keras 3 #1975)
• Recommonmark is no longer updated and it breaks for 3.12 due to newer versions of sphinx (Problem with conda installation on Mac M3 #1967 (comment)) (in Docs for new commondata format #1708 sphinx is pinned to 5)
• Curio is no longer updated but the version of reportengine we use depends on it.. Might be fixed by moving to dask but there are some small changes in reportengine needed for that Update reportengine dependencies reportengine#61

Please add any other issues as you find them.

[RoyStegeman]

@achiefa can you take care of recommonmark? It's a matter of updating the documentation so that it's no longer required at all. If you'd like we can discuss together what needs to be done exactly.

[achiefa]

@RoyStegeman yes, I'd like to discuss it together. But in principle I would say yes.

[scarlehoff]

I've pinned sphinx in #1708, it seems that version 5 still works with recommonmark (even in 3.12) so that it can be used.

We still should remove all markdown files because this is only a temporary patch and will eventually break as well.